The invention relates to a plasma sputtering installation of the type having a target at an electric potential and a microwave source which feeds microwaves into the plasma volume over the target.
Installations of this type are used, for example, when applying thin layers on glass panes, films of synthetic materials or the like. These thin layers often serve very different purposes. For example, coated windows reflect or transmit light of particular wavelengths while coated plastic eye glasses receive a harder surface. In the case of compact disks, the issue is the reflection or non-reflection of laser beams, which, in turn, comprises information about music or voice content.
For applying thin layers, numerous processes have already been suggested, of which only galvanotechnics and coating out of a plasma are mentioned.
In coating out of a plasma the so-called sputtering technique has assumed great importance. Herein a target comprising a particular metal is disposed at an electrode and sputtered by impinging charged particles, for example ions. The sputtered particles are subsequently deposited on a substrate, for example a pane of glass.
In a known configuration for generating a transparent and electrically conducting layer comprising In--O, Sn--O, Zn--O, Cd--Sn--O or Cd--In--O, target material is sputtered wherein the strength of a magnetic field on the surface of the target is 600 Oe or higher and wherein the target is supplied with a dc voltage on which is superimposed a high-frequency alternating voltage (EP-A-O447 850). Of the target materials used here, the target based on In--O with a small quantity of Sn added--often called ITO--yields a layer with a very low resistance value.
In order to improve the sputtering effect, it is further known to feed microwaves into the plasma (U.S. Pat. No. 4,610,770, U.S. Pat. No. 4,721,553, DE-A-3 920 834, JP-A-62 170 475, JP Patents Abstracts C-469, Jan. 16, 1988, Vol. 12, No. 15; JP-A-63 297 557, JP Patents Abstracts C-581, Apr. 4, 1989, Vol. 13, No. 134). Herein, microwaves are introduced into the plasma region either parallel or perpendicularly to the substrate surface.
DE-A 42 30 290 and DE-A 42 30 291 suggest irradiation of microwaves into the plasma. However, the discharge voltages during the sputtering of the target, in particular during ITO sputtering, are herein still relatively high.